This invention relates to a method of manufacturing liquid crystal devices.
A variety of solid display devices replacing CRTs have been developed, such as liquid crystal displays, displays utilizing electrochromic phenomena and displays utilizing gas discharge. Particularly, liquid crystal devices have been found to be suitable for practical use because of quick response and high power efficiency.
In recent years, however, along with the increasing information to be treated, the number of pixels has been monotonically increasing. While the quality of products can be kept if the displays have a small number of pixels with twisted nematic liquid crystal, the quality of a displayed image necessarily becomes poor due to cross-talk and other causes when the displays are designed to have a large number of pixels, e.g. 640.times.400. Attempts have been made; hitherto to deal with this, for example, making use of the SBE mode for twisted nematic liquid crystal devices or making use of semiconductor devices for switching pixels.
When thin film transistors are used to drive TN active matrix liquid crystal displays, the production cost becomes high because of the formation process of the transistors incurring additional costs and the low production yield of the transistors, whereas the provision of the transistors makes the quality of a displayed image high. Further, the response speed of such a liquid crystal display is low, and therefore it is not suitable for use of such an application that quick response is desired.
Displays utilizing ferroelectric liquid crystals have been proposed by N. A. Clark et al. to realize quick response. (Japanese Patent Disclosure No. sho56-107216). In liquid crystal devices of this type, liquid crystal molecules take one of two states (I) and (II) as illustrated in FIG. 1. The direction of anisotropy of the liquid crystal is the direction of the long axis (director) of the molecules. The angle .theta. between the director and the central line is termed the tilted angle. FIG. 3 shows an example of a signal which is applied to the liquid crystal display in order to change the states of ferroelectric liquid crystal molecules.
The molecule takes either of the two states in accordance with the direction of the applied electric field normal to the plane of the drawing sheet, by virtue of the dielectric moment of the molecule which is also normal to the plane of the drawing sheet.
In liquid crystal devices, ferroelectric liquid crystal is sandwiched by a pair of substrates having an electrode arrangement on the inside surfaces and the molecules are aligned parallel to the inside surfaces of the substrates contiguous to the liquid crystal. The liquid crystal devices have bistability by virtue of the interaction between the inside surfaces and the liquid crystal molecules.
On the other hand, such ferroelectric liquid crystal molecules have a tendency to form spirals which hinder the formation of anisotropic structure in the liquid crystal layer. To unwind the spiral the distance between the substrates is selected to be 1-3 microns. The short distance makes it difficult to manufacture such liquid crystal displays.
Furthermore, the low production yield of active devices for driving the liquid crystal displays has posed a difficult problem in attempts to reduce the production cost.